The long range objective of this study is to extend our knowledge of neuronal mechanisms by identifying the specific connections of monoamine systems with other neuronal systems using chemical neuroanatomical techniques. Such studies form the basis for understanding the regulation of sensory, autonomic, endocrine, and motor activity. The specific aims of the present study are (1) to identify specific connections of catecholamine systems with the spinothalamic system and (2) to investigate other potential sites of interaction with the spinothalamic cells in the spinal cord at the thalamus and in the brain-stem. Immunocytochemical techniques will be used to define the neurotransmitter/neuromodulator systems and axoplasmic transport tracing techniques will be employed to identify projections of these systems. The combined sequential use of such chemical anatomical tools using two chromagens can provide specific information about (1) terminations associated with cell bodies of other systems, (2) common terminal fields, and colocalization within the same neuron or terminal. More precise definition of anatomical connectivities is now possible with the use of these dual labels in vibratome sections which are then flat embedded in plastic resin and sectioned at 1 micron for analysis at light level. This method allows expeditious analysis of specific connectivities while maintaining the three dimensional relationship not readily apparent in ultrastructural studies. The relationships observed at the light level may be confirmed in the same preparation at the ultrastructural level. Serial thin sections will be examined and the perimeter of spinothalamic tract neurons photographed. Analysis of terminal types including immunocytochemically identified terminal will be performed from the reconstructed photographic montages of the neurons (x24,270). Terminal types will be classified according to morphological criteria and using stereological methods.